Synchronization of radio units in radio access networks

Abstract

A distributed radio frequency communication system facilitates communication between wireless terminals and a core network. The system includes a group of remote radio units (RRUs). Each RRU of the group of RRUs is coupled to an antenna to communicate with at least some of the mobile terminals and includes electronic circuitry to perform at least a first portion of a first-level protocol of a radio access network (RAN) and communicate over a fronthaul link. The system also includes a baseband unit (BBU) coupled to the core network and the fronthaul link, and communicably coupled to the group of RRUs over the fronthaul link. The RRU receives a synchronization-assisting radio-frequency signal and sends information derived from that signal to the BBU. The BBU processes the information to determine synchronization instructions which are then used to adjust a local clock in the RRU.

What is claimed is: 
     
       1. A method for synchronizing a remote radio unit (RRU) in a distributed radio access network (RAN), the method comprising:
 generating, at a baseband unit (BBU) in the RAN, synchronization instructions to synchronize a local clock of a synchronization device to the RAN, wherein the synchronization device is coupled to the BBU using a first fronthaul link and is coupled to the RRU using a second fronthaul link; 
 sending the synchronization instructions from the BBU to the synchronization device over the first fronthaul link; and 
 controlling a local clock of the synchronization device using the synchronization instructions; and 
 controlling, by the synchronization device, a local clock in the RRU using the second fronthaul link. 
 
     
     
       2. The method of  claim 1 , further comprising:
 communicating, by the RRU, with the at least one wireless terminal using radio-frequency signals; 
 performing at least a first portion of a first-level protocol of the RAN within the RRU; and 
 communicating data of the communication with the at least one wireless terminal from the RRU over the first fronthaul link and second communication with the BBU via the synchronization device. 
 
     
     
       3. The method of  claim 2 , wherein the RAN protocol comprises an Evolved Universal Terrestrial Radio Access Network (E-UTRAN); and
 the first-level protocol comprises an Evolved Universal Terrestrial Radio Access (E-UTRA) physical-layer (PHY) protocol. 
 
     
     
       4. The method of  claim 1 , wherein the second fronthaul link is a synchronous fronthaul link and the local clock in the RRU is locked to the second fronthaul link. 
     
     
       5. The method of  claim 1 , wherein the second fronthaul link uses a common public radio interface (CPRI) protocol and CPRI synchronization is used to control the local clock in the RRU. 
     
     
       6. The method of  claim 1 , further comprising:
 using the synchronization instructions to control the local clock in the RRU. 
 
     
     
       7. The method of  claim 6 , wherein the synchronization instructions comprise an instruction to change a frequency or a phase of the local clock at least one of the synchronization device or RRU. 
     
     
       8. The method of  claim 6 , wherein the first fronthaul link is an asynchronous fronthaul link, the method further comprising adjusting the local clock in the synchronization device based on the synchronization instructions to control the local clock in the synchronization device. 
     
     
       9. The system of  claim 8 , wherein the asynchronous fronthaul link utilizes an internet protocol (IP). 
     
     
       10. The method of  claim 1 , further comprising:
 receiving a synchronization-assisting radio-frequency signal through an antenna at the synchronization device; and 
 sending information derived from the synchronization-assisting radio-frequency signal from the synchronization device to the BBU over the first fronthaul link. 
 
     
     
       11. The method of  claim 10 , wherein the synchronization-assisting radio-frequency signal comprises a GPS satellite signal, a downlink signal from a cellular base station, a television broadcast signal, an uplink signal from a cellular terminal, or a time broadcast signal. 
     
     
       12. The method of  claim 10 , wherein the RRU is a first RRU and the synchronization-assisting radio-frequency signal comprises a signal from a second RRU. 
     
     
       13. The method of  claim 12 , wherein the signal from the second RRU comprises a downlink signal or a dedicated beacon signal. 
     
     
       14. The method of  claim 10 , further comprising:
 receiving control instructions from the BBU over the first fronthaul link at the synchronization device; and 
 controlling at least one aspect of the receiving of the synchronization-assisting radio-frequency signal or the derivation of the information from the synchronization- assisting radio-frequency signal based on the control instructions. 
 
     
     
       15. The method of  claim 14 , the control instructions comprising:
 an instruction to set a receive frequency for a radio-frequency receiver in the synchronization device based on the control instructions to receive the synchronization-assisting radio-frequency signal through the radio frequency receiver. 
 
     
     
       16. The method of  claim 14 , the control instructions comprising:
 an instruction to set a time period of the synchronization-assisting radio-frequency signal, based on the control instructions, to use to create the information derived from the synchronization-assisting radio-frequency signal. 
 
     
     
       17. The method of  claim 10 , further comprising:
 compressing a block of digital samples captured from the received synchronization-assisting radio-frequency signal to create the information derived from the synchronization-assisting radio-frequency signal. 
 
     
     
       18. The method of  claim 1 , further comprising:
 receiving first fronthaul data from the BBU via the first fronthaul link using a first fronthaul protocol; 
 converting the first fronthaul data to second fronthaul data; and 
 forwarding the second fronthaul data to the RRU via the second fronthaul link using a second fronthaul protocol. 
 
     
     
       19. The method of  claim 18 , wherein the first fronthaul protocol comprises a fronthaul-over-internet-protocol (FIP) based fronthaul protocol and the second fronthaul protocol comprises a common public radio interface (CPRI) based fronthaul protocol. 
     
     
       20. A synchronization device comprising:
 a processor; 
 a local clock coupled to the processor; 
 a first interface between a first fronthaul link and the processor; 
 a second interface between a second fronthaul link and the processor; and 
 at least one non-transitory machine readable medium, coupled to the processor, and comprising one or more instructions that in response to being executed by the processor cause the synchronization device to:
 receive synchronization instructions from; 
 a baseband unit (BBU) of a distributed radio access network (RAN) using the first interface; 
 
 control the local clock of the synchronization device using the synchronization instructions; and 
 control a local clock in a remote radio unit (RRU) of the RAN using the second interface. 
 
     
     
       21. The synchronization device of  claim 20 , wherein the one or more instructions, in response to being executed by the processor, further cause the synchronization device to:
 use the synchronization instructions to control the local clock in the RRU. 
 
     
     
       22. The synchronization device of  claim 20 , wherein the one or more instructions, in response to being executed by the processor, further cause the synchronization device to:
 receive first fronthaul data from the BBU via the first fronthaul link using a first fronthaul protocol; 
 convert the first fronthaul data to second fronthaul data; and 
 forward the second fronthaul data to the RRU via the second fronthaul link using a second fronthaul protocol. 
 
     
     
       23. The synchronization device of  claim 22 , wherein the first fronthaul protocol comprises a fronthaul-over-internet-protocol (FIP) based fronthaul protocol and the second fronthaul protocol comprises a common public radio interface (CPRI) based fronthaul protocol. 
     
     
       24. At least one non-transitory machine readable medium comprising one or more instructions that in response to being executed by a processor of a synchronization device of a distributed radio access network (RAN) cause a remote radio unit (RRU) to:
 receive a synchronization instructions from a baseband unit (BBU) of the RAN using a first fronthaul link that couples the synchronization device to the BBU; 
 control a local clock of the synchronization device using the synchronization instructions; and 
 control a local clock in the RRU of the RAN using a second fronthaul link that couples the synchronization device to the RRU. 
 
     
     
       25. The at least one non-transitory machine readable medium of  claim 24 , wherein the one or more instructions, in response to being executed by the processor, further cause the synchronization device to:
 use the synchronization instructions to control the local clock in the RRU. 
 
     
     
       26. The at least one non-transitory machine readable medium of  claim 24 , wherein the synchronization instructions comprise an instruction to change a frequency or a phase of the local clock of the synchronization device. 
     
     
       27. The at least one non-transitory machine readable medium of  claim 24 , wherein the one or more instructions, in response to being executed by the processor, further cause the RRU to:
 receiving a synchronization-assisting radio-frequency signal through an antenna at the synchronization device; and 
 sending information derived from the synchronization-assisting radio-frequency signal from the synchronization device to the BBU over the first fronthaul link. 
 
     
     
       28. The at least one non-transitory machine readable medium of  claim 24 , wherein the one or more instructions, in response to being executed by the processor, further cause the synchronization device to:
 receive first fronthaul data from the BBU via the first fronthaul link using a first fronthaul protocol; 
 convert the first fronthaul data to second fronthaul data; and 
 forward the second fronthaul data to the RRU via the second fronthaul link using a second fronthaul protocol. 
 
     
     
       29. The at least one non-transitory machine readable medium of  claim 28 , wherein the first fronthaul protocol comprises a fronthaul-over-internet-protocol (FIP) based fronthaul protocol and the second fronthaul protocol comprises a common public radio interface (CPRI) based fronthaul protocol.